The present invention relates to an ink jet recording head used with an ink jet printer, or the like.
In an ink jet recording head in a related art, for example, in an ink jet recording head using a piezoelectric vibrator as an electromechanical transducing element, a channel formation substrate and a vibration plate are laminated on a nozzle plate with a plurality of nozzle orifices arranged in rows, forming a channel unit, which is joined to a case.
That is, the channel formation substrate is formed with pressure generating chambers like through holes communicating with the nozzle orifices, a common ink reservoir for storing ink supplied to the pressure generating chambers, ink supply ports through which the common ink reservoir and the pressure generating chambers communicate with each other, and the like, the members being defined by partition walls. The vibration plate consists of a thick portion (island portion) and a thin portion (film portion) surrounding the thick portion. Specifically, a composite plate comprising a resin film 3 to 10 xcexcm thick and a stainless plate 20 to 50 xcexcm thick is etched, forming the island portion with a stainless portion left and the film portion.
A nozzle plate is bonded to one side of the channel formation substrate and the vibration plate is bonded to an opposite side, thereby forming the channel unit. Piezoelectric vibrators are placed corresponding to the pressure generating chambers and are fixed to the case and the channel unit is attached to the case, whereby the piezoelectric vibrators are abutted against predetermined portions (island portions) of the vibration plate of the pressure generating chambers corresponding to the piezoelectric vibrators and are fixed.
With the described recording head, ink is supplied from the common ink reservoir to each pressure generating chamber and the vibration plate is bent by the action of the piezoelectric vibrator for pressurizing the pressure generating chamber, so that an ink drop is jetted through the nozzle orifice by the pressure.
For this kind of recording head, in recent years, an extremely high resolution, such as 720 dpi or 1440 dpi, has been demanded; moreover, a high resolution has been demanded using four color inks of black, yellow, magenta, and cyan. Thus, it becomes necessary to jet ink drops made small with several ng per dot and therefore the characteristic vibration frequency of ink in the pressure generating chamber must be raised.
However, if an attempt is made to raise the characteristic vibration frequency, the characteristic vibration frequency f varies largely depending on compliance (easy-to-deform property; represented by a unit of [m3/Pa]) of the recording head. The relation between f and C is represented by the following equation:   f  =      1          2      ⁢              xe2x80x83            ⁢      π      ⁢              MC            
here, M denotes inertance of the mass of a medium per unit length (described later). Therefore, tolerance variation at the manufacturing stage seriously affects the jet characteristic of the recording head.
That is, very high accuracy of finishing in xcexcm units is required when cavities of the pressure generating chambers, the ink supply ports, etc., of the channel formation substrate are formed or the vibration plate is formed with the island portion.
However, when the island and film portions are formed by etching metal, variations of xc2x120 xcexcm in the longitudinal direction of the island portion and xc2x17 xcexcm in the widthwise direction occur and the compliance C varies due to area variations in the film portion.
The component of the compliance C of the recording head can be roughly classified into compliance C.ink of ink in the pressure generating chambers and compliance C.str of pressure generating chamber components such as the partition walls, the vibration plate, and the nozzle plate forming the pressure generating chambers.
C.ink is proportional to the pressure generating chamber volume which depends mainly on the accuracy of finishing of the channel formation substrate. Specifically, required accuracy can be provided by applying an anisotropic etching technique of silicon.
However, in the film portion of the vibration plate (portion where C.str makes up the greatest percentage), it is hard to lessen the variations in the compliance caused by tolerance variations as described above.
In the recording head in the related art, the ink compliance C.ink makes up 20% to 45% of the compliance of the whole head, compliance C.cav of the partition walls and nozzle plates of the pressure generating chambers makes up 2%, and compliance C.film of the vibration plate makes up 53% to 78%; the compliance C.str of the pressure generating chamber components (C.cav+C.film) makes up about 50% to 80%.
Thus, if the recording head is made up of the vibration plate, the channel formation substrate, etc., worked under the tolerance as described above, it is not easy to place the compliance for each assembled recording head in a predetermined range; particularly, the recording head compliance largely varies depending on how the vibration plate is worked.
The recording head with the compliance C.str of the pressure generating chamber components out of a predetermined range becomes a defective piece. Therefore, yield lowers if an attempt is made to raise the characteristic vibration frequency of ink in the pressure generating chamber for providing a high resolution as mentioned above.
It is therefore an object of the invention to provide an ink jet recording head for making it possible to decrease variations in the compliance of the recording head without depending only on accuracy of finishing and suppress occurrence of recording heads which become defective pieces for improving yield.
In order to achieve the above object, there is provided an ink jet recording head comprising:
an electromechanical transducing element;
a nozzle plate provided with a plurality of nozzle orifices;
a channel forming substrate including:
partition walls defining a plurality of pressure generating chambers arranged so as to correspond to the nozzle orifices; and
ink supply ports for supplying ink into associated pressure generating chambers;
a vibration plate composing a part of an inner wall of the respective pressure generating chambers for being flexed by deformation of the electromechanical transducing element to varying the volume of the respective pressure generating chambers; and
a compliance component including:
a first compliance component comprising at least one member composing the respective pressure generating chambers; and
a second compliance component comprising the ink in the respective pressure generating chambers, and being larger than the first compliance component.
For example, the first compliance component may include the partition walls and the vibrating plate.
Specifically, the second compliance component accounts for more than 45% of the compliance component.
Accordingly, the percentage of the compliance varying depending on the accuracy of finishing of the channel formation substrate and the vibration plate lessens relatively. Therefore, if the parts are worked under the tolerance in the related art, the compliance of the recording head is less affected. Thus, the compliance for each manufactured recording head easily enters a predetermined range, so that occurrence of defective pieces can be suppressed for improving yield.
In order to increase the relative percentage of the second compliance component, the volume of the respective pressure generating chamber is increased.
Accordingly, the compliance of the recording head can be stabilized without making the accuracy of finishing specially strict.
In order to increase the volume of the respective pressure generating chambers, thickness of the channel forming substrate is thickened.
Accordingly, if a silicon wafer is used to form the channel formation substrate, rapid cost increase can be avoided and miniaturization of the recording head can be maintained.
In order to obtain the relative higher percentage of the second compliance component, thickness of the vibrating plate is thickened so as to lower a relative percentage of the first compliance component.
Accordingly, stabilization of the compliance of the recording head can be accomplished easily.
In the recording head, the vibration plate is composed of a resin film and a metal layer.
Accordingly, it is easy to relatively lower the percentage of the compliance of the vibration plate by using a thick resin film.
In the recording head, the electromechanical transducing element is a piezoelectric vibrator.
In the recording head, the pressure generating chambers and the ink supply ports are formed by etching a silicon wafer anisotropically.
Accordingly, extremely high accuracy of finishing is provided easily.
According to the present invention, there is provided an image recording apparatus comprising an ink jet recording head as described above.
In the recording head, the respective pressure generating chambers may be partitioned into a plurality of chambers in a deforming direction of the electromechanical transducing element which are communicated with each other by a through hole.